After assembling engines and car bodies a conducting connection between the different aggregates by water-, fuel-, air- and pressure lines has to be accomplished. Due to the minor amount of space under the hood of an automobile, hoses used for the connection of engine, cooler, radiator and fuel tank, etc. have to be individually adapted to the various types of engine and car body. Depending on the space available under the vehicle hood the shape of the hoses may be very complex.
Consequently, there is a strong need for hoses, in particular, coolant hoses and/or fuel lines, having a complex shape and a good resistance to the rough environmental conditions in applications under the hood.
Automotive hoses are exposed to exceedingly harsh environments. Factors including varying pressures and temperatures at different points of the hose, varying diameters of different hoses in a particular circuit, as well as chemical exposure result in the need for highly rigorous hoses.
Currently some fuel lines and coolant hoses are made by classical straight extrusion or co-extrusion in nylon/TPV configuration; the shaping of the tubes occurs off-line using various thermo-forming or thermo-fixation techniques. Off-line shaping is a cost and labor intensive process since the green tubes to be shaped are manually fitted into the shaping equipment and afterwards the shaped tubes have to be removed by hand. Due to the thermal treatment in open air some degradation at the surface of the articles may occur.
Some of the commercially available fuel lines and coolant hoses are partially corrugated. However, these corrugated sections may offer more resistance to flow than tubes that are smooth on the inside surface. In addition such sections may cause the formation of deposits.
U.S. Pat. No. 5,336,349 relates to an apparatus for providing the surface of an article, for instance a car wind screen, with a profiled gasket by supplying a thermoplastic elastomer via an extruder and a heated pressure hose to a heated extrusion die. The extrusion die is guided by a robot, and the elastomer is extruded and laid by means of the extrusion die onto the surface. Therefore, the shape of the obtained profile is mainly dependent on the topography of the supporting surface.
Due to the low green-strength of several important polymers, for instance of polyamides used for the manufacturing of automotive fuel lines, the process disclosed by U.S. Pat. No. 5,336,349 can not be applied when three dimensional shaped free-standing articles are desired since a free-shaping of the extrudate independent from the underlying surface can not be accomplished by the disclosed method. In case of such polymers having insufficient green strength the tubular extrudate would immediately collapse after leaving the die orifice.
Therefore, it has been an object underlying the present invention to provide a method for the free shaping of hoses made from materials having low green-strength.
It has surprisingly been found that this object can be accomplished by supporting a polymeric layer obtained from a polymer having insufficient green-strength by a second adjacent support layer of adequate green-strength. For instance, a layer of a polymer having adequate green-strength on the inside and/or the outside of an extruded tubular article of a polymer having insufficient green-strength avoids collapsing of the supported layer after leaving the die orifice. Both layers (the supporting layer and the supported layer) may be formed in one shot by co-extruding the polymers and by a simultaneous shaping operation in order to obtain the desired tubular articles of complex shape.